Practical experience shows that a passage of current through a bearing can lead to a damage of the bearing. Therefore a need for electrically insulated bearings exists, particularly for electrically insulated bearing rings.
From prior art ceramic coatings are known that are provided as an electrically insulating coating on a metallic, and thus conductive body of a bearing ring, therefore suppressing the passage of electric current through the bearing, as is, for example, defined in the German patent application DE 10 2010 015 155 A1 or DE 10 2009 014 753 A1.
Furthermore electrically insulating coatings consist mostly of an aluminum oxide. The electrically insulating layer of aluminum oxide is very hard. However, the dielectric constant of this type of coating is higher than of insulating plastic materials.
In addition, such electrically insulating coatings are shock-sensitive and can burst easily, so that a small-grained ceramic material is mounted on a bearing in a manner through which a ceramic coating is formed with a proportion of pores considerably less than 10%. To prevent an ingression of moisture through the pores in the ceramic coating, the ceramic coating with its pores is sealed. The layer thickness of such electrically insulating coatings is, in practice, currently between 0.1 and 0.4 mm.
As there are currently many problems concerning the passage of high-frequency currents through bearings, an enhancement is needed to secure a better insulation against high-frequency currents.